1. Field of the Invention
This invention relates to cationic nitriles and to an improved bleach composition and a bleaching detergent composition containing said cationic nitrile to serve as a peroxyacid bleach precursor.
2. The Related Art
It is known that the bleach activity of hydrogen peroxide bleach compounds, such as the perborates, percarbonates, persilicates and perphosphates, can be improved so as to become effective at lower wash temperatures, i.e. at or below 60.degree. C., by the use of peroxyacid bleach precursors, often also referred to as bleach activators.
Numerous substances have been disclosed and proposed in the art as usable peroxyacid bleach precursors. Conventionally, these precursors are reactive organic compounds having an O-acyl or N-acyl group, such as carboxylic acid esters, that in alkaline solutions containing a source of hydrogen peroxide will generate the corresponding peroxyacids, a reaction which is also referred to as perhydrolysis. They can be represented by the following general formula: ##STR1## wherein R can be any suitable radical forming the RCO (acyl) radical and L is a suitable leaving group. It is believed that the reaction with hydrogen peroxide proceeds as follows: EQU RCO--L+OOH.sup.- .fwdarw.RCO--OOH+L.sup.-
A leaving group is thus any group that is displaced from the peroxyacid bleach precursor as a consequence of nucleophilic attack on the precursor by the hydroperoxide anion. This, i.e. the perhydrolysis reaction, results in the formation of the peroxyacid. Generally, for a group to be a suitable leaving group, it must exert an electron-attracting effect, which facilitates expulsion of the leaving group from the tetrahydral intermediate formed by nucleophilic attack by the hydroperoxide anion. Many and diverse leaving group structures have been described in the patent literature (see, for example, EP-A-0120591). Not only do leaving groups add extra weight to bleach precursors of the conventional type but, once expelled from the precursor as a consequence of nucleophilic attack, they will remain as substantially useless by-products in the bleach solution.
Examples of the most representative precursors of this broad class include N,N,N',N'-tetraacetyl ethylene diamine (TAED), glucose pentaacetate (GPA), xylose tetraacetate (TAX), sodium-4-benzoyloxy benzene sulphonate (SBOBS), sodiumtrimethyl hexanoyloxy benzene sulphonate (STHOBS), tetraacetyl glucoluril (TAGU), tetraacetyl cyanuric acid (TACA), di-N-acetyldimethyl glyoxine (ADMG) and I-phenyl-3-acetylhydantoin (PAH)--see, for example, GB-A-836,988; GB-A-907,356; EP-A-0098129 and EP-A-0120591, which represent only a small part of the large amount of patent literature disclosing precursors.
Recently, cationic peroxyacid precursors have attracted interest of Research workers as substantive and highly effective bleach activators. The same above-indicated general formula also applies to the general class of cationic peroxyacid precursors, but with the special feature of R being a radical containing a quaternary ammonium or quaternary phosphonium group, i.e. ##STR2## Such cationic peroxyacid precursors are described in, for example, GB-A-1,382,594; U.S. Pat. No. 4,751,015; EP-A-0284292 and EP-A-0331229.
Cationic nitriles form a special class of cationic peroxyacid precursors. These compounds are described in EP-A-0303520 and are said to have at least one of the following groups (a) and (b) : ##STR3##
It is suggested here that the presence of the cationic group .tbd.N.sup.+ --CH.sub.2 CN is essential for the compound to exert its function as effective peroxyacid precursor.
An advantage of these compounds is that they do not contain a leaving group as has routinely been the convention. It is believed that, upon perhydrolysis, they generate a peroxyimidic acid as the highly reactive bleaching species, without the loss of weight involved in having an attached leaving group, as diagrammatically illustrated in the following reaction: ##STR4##
A serious drawback of the cationic nitriles of the art, however, is their highly hygroscopic nature. It has been observed that the cationic nitriles of the art, e.g. (CH.sub.3).sub.3 N.sup.+ -CH.sub.2 CN Cl.sup.-, take up water fairly quickly and deliquesce already upon exposure to an atmosphere of relative humidity of less than about 30% at ambient temperatures. Eventually they will hydrolyze and form the corresponding inactive amide, e.g. ##STR5##
It is therefore an object of the invention to provide an improved and effective cationic peroxyacid precursor without a leaving group, wherein the above drawback is mitigated or even removed, thereby enabling its commercial exploitation.
Having a cationic group, cationic nitriles, just like any other cationic compound, require in their existence the presence of a counter-anion X.sup.-, such as Cl.sup.-, I.sup.-, NO.sub.3.sup.- and the like, Cl.sup.- being the most common anion.